Position control device for a hydraulic actuator and interface plate for a servovalve implementing such a device

ABSTRACT

The invention relates to a position control device for a hydraulic actuator, such device comprising a hydraulic circuit comprising a pump supplying the two chambers of the actuator from a hydraulic tank or reserve by means of a servovalve, each outlet of the servovalve being connected to a chamber of the actuator by means of a non return valve. This such device is characterized in that at least one of the outlets of the servovalve connected a chamber of the actuator is also connected to the hydraulic tank by a calibrated nozzle upstream of the non return valve. The invention also relates to an interface plate for a servovalve allowing such a device to be implemented. The invention can namely be applied to the open loop and/or closed loop servo control of the laying of a gun barrel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The technical scope of the invention is that of devices enabling thepositioning of a hydraulic actuator to be controlled.

These devices generally comprise a hydraulic circuit incorporating apump (for example of variable size) supplying one or other of the twochambers of the actuator by means of a servovalve.

2. Description of the Related Art

The servovalve is a classical off-the-shelf component and comprises aslide made mobile by a torque motor. This slide may occupy at leastthree different positions: one central position in which the circuitsare closed and two symmetrical positions allowing one or other of thechambers of the actuator to be connected to the hydraulic pump whereasthe other chamber is connected to a hydraulic tank or reserve. The slidemay also occupy, according to the control given by the torque motor, anyintermediate position between the central position and one or other ofthe extreme positions, each intermediate position corresponding to adifferent fluid flow provided by the servovalve.

Such a servovalve is classically used in closed-loop actuator controls,that is to say controls with position servo control. Such a servovalvemay also be used to control an open loop actuator, that is to say onewith no position servo control.

In any event, so as to avoid the hydraulic pump working constantly, acontrolled non-return valve is positioned between each chamber of theactuator and the servovalve. Thus, the pressure in each chamber of theactuator is maintained regardless of the supply level. This non-returnvalve, moreover, improves the positioning accuracy of the open loopactuator. However, this solution has disadvantages, both when operatingin closed loop or open loop. Indeed, the sections of the actuatorchambers are different (notably because of the presence of the cylinderrod in one of the chambers). This results in a small jolt at the end ofthe positioning process leading to an inaccuracy in the finalpositioning of the actuator.

Thus, when the actuator is a cylinder to ensure the elevation laying ofa gun, the elevation laying angle obtained is erroneous with respect tothe instruction given and the gun is incorrectly laid.

Moreover, under open loop operation positioning of the actuator can beseen to drift.

The aim of the present invention is to overcome such drawbacks byproposing a control device to position a hydraulic actuator able to beoperated both in closed and open loop whilst ensuring positioningaccuracy and laying speed.

SUMMARY OF THE INVENTION

The invention also enables this positioning to be ensured using standardoff-the-shelf inexpensive components.

Thus, the invention relates to a position control device for a hydraulicactuator, such device comprising a hydraulic circuit comprising a pumpsupplying the two chambers of the actuator from a hydraulic tank orreserve by means of a servovalve, each outlet of the servovalve beingconnected to a chamber of the actuator by means of a non return valve,such device wherein at least one of the outlets of the servovalveconnected a chamber of the actuator is also connected to the hydraulictank by a calibrated nozzle upstream of the non return valve.

The device may comprise a calibrated nozzle connecting each outlet ofthe servovalve to the hydraulic tank.

The invention also relates to a servovalve interface plate enabling thisdevice to be implemented at low cost using standard inexpensivecomponents.

This plate incorporates at least four transversal drill holes intendedto cooperate with the four hydraulic ports of the servovalve, that is tosay a supply of pressurised fluid via a pump, an outlet to a reservetank, a first control path for a first chamber of the actuator and asecond control path for a second chamber of the actuator, such platewherein it incorporates at least one leak circuit connecting one of thecontrol paths to the tank outlet, such circuit in which is positioned acalibrated nozzle.

The servovalve interface plate may incorporate two leak circuitscomprising a calibrated nozzle, each circuit connecting one of thecontrol paths to the tank outlet.

The leak circuit(s) will advantageously be made in the form of holesperpendicular to one another and to the transversal drill holescorresponding to the different paths.

The outward opening of each hole may be stopped by a plug.

The nozzle(s) may be made in the form of screws having a calibratedaxial orifice.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the invention will become more apparent from thefollowing description of a particular embodiment of the invention, suchdescription made with reference to the appended drawings, in which:

FIG. 1 is a simplified hydraulic schema of a control device according tothe invention,

FIG. 2 is a simplified schema of the interface plate according to theinvention,

FIGS. 3 a, 3 b and 3 c are three views of an embodiment of the interfaceplate, FIGS. 3 a and 3 b being sections along planes AA and BBrespectively in FIG. 3 c.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the schema of a device 1 to control the position of ahydraulic actuator 2, for example a cylinder comprising a piston 2 cintegral with a rod 2 d and delimiting two chambers 2 a and 2 b. Thecylinder ensures the elevation or traverse laying of a gun barrel (notshown). This device comprises a hydraulic circuit incorporating a pump 3supplying the two chambers 2 a, 2 b of the actuator 2 by means of aservovalve 4.

The latter is a classical off-the-shelf 4-way flow servovalve.

It incorporates four ports conventionally termed A, B, P and T. Port Tis intended for the return to the tank 5, inlet port P for thereplenishment in fluid by the pump 3, outlet ports A and B beingintended to connect the servovalve 4 to the two chambers 2 a and 2 b ofthe cylinder 2.

The pump 3 is thus connected by upstream ducting 6 a to the hydraulictank 5 (or fluid reserve) and discharges by downstream ducting 6 b tothe inlet port P of the servovalve 4.

The servovalve 4 is conventionally shown in FIG. 1 in its closedposition (median block 4c in the circuit) in which the four ports A, B,P and T are blocked.

The servovalve slide may occupy at least two different active extremepositions:

-   -   a first one (left block 4 a in the circuit) in which the inlet        port P is connected to the outlet port 1 whereas the other        outlet B is connected to the tank 5 via port T.    -   a second one (right block 4 b in the circuit) in which the inlet        port P is connected to the outlet port B whereas the other        outlet port A is connected to the tank 5 via port T.

The displacements of the servovalve slide are controlled classically bya torque motor 4d integrated into the servovalve, such torque motorpiloted by an electronic control unit 7.

The extreme positions 4 a, 4 b correspond to the maximal fluiddischarges supplied by the servo vale. The slide may classically occupyintermediate positions between the closed position and one or other ofthe two extreme positions. These intermediate positions correspond todifferent fluid discharges transmitted according to one or other of thecontrol paths.

The outlet ports A and B of the servovalve 4 are connected by ducting 8a and 8 b to chambers 2 a and 2 b of the cylinder 2 by means of twocontrolled non return valves 9 a, 9 b.

These non-return valves are presented here in the form of a singlehydraulic block 9 incorporating four outlets C, D, E and F. Each valve 9a, 9 b comprises a ball applied to a seat by the pressure in theactuator 2 side. The ball may be moved away from the seat by a controlpressure.

Valve 9 a is positioned between outlets C and E and connects chamber 9 aof the actuator and port A of the servovalve 4. Valve 9 b is positionedbetween outlets D and F and connected chamber 2 b of the actuator andport B of the servovalve. Hydraulic links 9 c and 9 d (shown in dottedlines) ensure the control of valves 9 b and 9 a respectively.

Thus, an arrival of pressure at D naturally flows towards F throughvalve 9 b and also lifts the ball of valve 9 a thereby allowing fluid topass from E to C. Inversely, an arrival of pressure at C flows towards Eand allows fluid to pass from F to D.

Valves 9 a and 9 b allow the cylinder 2 to hold its position whencontrolled in open or closed loop.

According to the invention, at least one calibrated nozzle is positionedconnecting one of outlet ports A or B of the servovalve 4 to thehydraulic tank 5.

In the embodiment shown in FIG. 1, two nozzles 10 a and 10 b areprovided.

A first nozzle 10 a is connected by ducting 11 a to ducting 8 a and itdrains part of the fluid circulating in it towards the tank 5.

A second nozzle 10 b is connected by ducting 11 b to ducting 8 b and itdrains part of the fluid circulating in it towards the tank 5.

The nozzles will be constituted by regulating nozzles of well definedcalibers. The calibers will be selected so as to ensure a drop inpressure in ducting 8 a or 8 b, which is inactive, without necessarilyreducing the discharge in ducting 8 b or 8 a, which controls themovement. Leak sections will be selected for the nozzles, for example,which enable a leak rate of between 4% and 7% of the fluid supplied bythe pump 3.

The nozzles 10 a and 10 b do not, therefore, perturb the normaloperation of the servovalve 4 since they cause no significant loss indischarge rate in ducting supplied by the pump 3.

Nevertheless, when the servovalve 4 is in the closed position shown inFIG. 1, the nozzles ensure a drop in the pressure of the fluid inducting 8 a and 8 b, upstream of the valve 9.

This drop in pressure allows the non-return valves 9 a and 9 b to bestabilized. Indeed, maintaining the pressure in the actuator's chambersis carried out by the balls applied onto their seats by the pressure onthe cylinder side. These balls are under the pressure of ducting 8 a and8 b on the other side of their seat.

Thanks to nozzles 10 a and 10 b, the pressure in ducting 8 a and 8 b atinlets C and D is lower than that respectively at inlets E and F. Theballs thus remain pressed onto their seats and any rebound, which couldlead to a jolt in the positioning of the cylinder, is avoided.

Laying may thus be carried out accurately when the positioning of thecylinder is servo controlled in a closed loop and that position is heldwithout drift when servo controlled in an open loop.

At least one nozzle with be provided connected to the ducting opposed tothe movement required to be accelerated. Preferably, two nozzles will beprovided, one connected to each ducting.

In practical terms, it is possible for the invention to be implementedby assembling ducting 11 a and 11 b such that is directly connected atany point in ducting 8 a and 8 b.

According to a preferred embodiment of the invention, it will beimplemented by providing a specific interface plate 13 integral with theservovalve 4.

FIG. 2 shows a simplified hydraulic schema of interface plate 13 andFIGS. 3 a, 3 b and 3 c show a particular embodiment of this interfaceplate.

A servovalve 4 is made, in practical terms, in the form of a componentincorporating a parallelepipedic base 12 fitted with inlet and outletopenings (or ports) A, B, T and P on a same upper face 12 a.

The interface plate 13 is thus also made in the form of aparallelepipedic block a lower face 13 a of which is intended to beapplied onto face 12 a of the servovalve. This face has four openingsTa, Aa, Ba and Pa intended to lie respectively opposite openings T, A, Band P of the servovalve. In a classical manner not shown, each opening(Ta, Aa, Ba, Pa) of interface plate 13 incorporates a countersink ableto house an O-ring. This O-ring will be applied during assembly againstface 12 a of the servo vale and will seal it.

An upper face 13 b of the plate 13 has four openings Tb, Ab, Bb and Pbto which the different ducting of the hydraulic circuit will beconnected. Ducting 8 a and 8 b leading to the cylinder are fastened toopenings Ab and Bb, ducting 6 b coming from the pump 3 is fastened toopening Pb and ducting 18, which returns to the hydraulic tank 5, isfastened to opening Tb. Fastening is made using appropriate hydraulicconnectors.

Face 13 b may also be applied against a hydraulic block (not shown)provided with holes corresponding to opening Tb, Ab, Bb and Pb. Thelatter openings will also be provided with countersinks (not shown) ableto house O-rings thereby ensuring sealing with respect to the block. Theblock will be connected using appropriate ducting to the cylinder, thepump and the tank.

The different openings of the lower face 13 a are connected to openingsin the upper face 13 b by holes drilled in the material of the plate 13.

Thus, opening Ta is connected to opening Tb by drill hole 14, opening Aais connected to opening Ab by drill hole 15, opening Ba is connected toopening Bb by drill hole 16 and opening Pa is connected to opening Pb bydrill hole 17.

Inside the plate, a first controlled hydraulic leak circuit 19 a isformed by a channel onto which a nozzle 10 a is positioned, whichconnects drill holes 15 and 14. The plate, moreover, encloses a secondleak circuit 19 a formed by another channel onto which is nozzle 10 b ispositioned. This second leak circuit 19 b connects drill holes 16 and14.

Thus, the plate 13 allows the servovalve 4 to be converted in anextremely simple manner to incorporate the nozzles proposed by theinvention. The hydraulic circuit may thus easily be modified without itbeing necessary to provide additional ducting.

As may be seen more specifically in FIGS. 3 a, 3 b and 3 c, the leakcircuits 19 a and 19 b are made in the shape of orthogonal holes. Suchan arrangement makes it easier to manufacture the interface plate 13.

So as to avoid any interference, the holes are made in two parallelplanes.

Thus, plane AA (FIG. 3 a) comprises two orthogonal holes 19 a 1 and 19 a2 which form the first leak circuit 19 a. Hole 19 a 2 encloses the firstnozzle 10 a, made in the form of a screw having a calibrated axialorifice.

Plane BB (FIG. 3 b) comprises four holes 19 b 1, 19 b 2, 19 b 3 and 19 b4 which are orthogonal two by two and thus form a rectangle. These fourholes constitute the second leak circuit 19 b. Hole 19 b 1 encloses thesecond nozzle 10 b also made is the form of a screw fitted with acalibrated axial orifice.

All the different holes are stopped and sealed by threaded plugs 20.

As may be seen, it is easy for the leak characteristics of the deviceaccording to the invention to be modified without the need for complexdismounting. The nozzles 10 a and 10 b merely have to be unscrewed andreplaced by nozzles having different leak diameters. The leak diametersof the nozzles will be selected according to the properties of theactuator, the load and the servo control circuit pressure in position.

Holes 21 passing right through the interface plate 13 are provided toallow the plate to be fastened onto the servovalve 4 by screws (notshown).

By way of a variant, it is naturally possible for only one nozzle to beprovided connecting one of the supply paths from the cylinder to thetank. In the case, the other nozzle will be replaced by a non-perforatedscrew.

This variant allows one of the movements of the cylinder to beaccelerated in a preferential manner.

1. A position control device for a hydraulic actuator, such devicecomprising a hydraulic circuit comprising a pump supplying the twochambers of said hydraulic actuator from a hydraulic tank or reserve bymeans of a servovalve, each outlet of said servovalve being connected toone of said chambers of said actuator by means of a non return valve,wherein at least one of said outlets of said servovalve connected one ofsaid chambers of said actuator is also connected to said hydraulic tankby a calibrated nozzle upstream of said non return valve.
 2. A positioncontrol device according to claim 1, wherein said device comprises acalibrated nozzle connecting said each outlet of said servovalve to saidhydraulic tank.
 3. An interface plate for a servovalve implemented inthe device according to one of claim 1, said plate incorporating atleast four transversal drill holes intended to cooperate with fourhydraulic openings or ports of said servovalve, thus to supply withpressurised fluid via a pump, an outlet to said tank, a first controlpath for a first chamber of said actuator and a second control path fora second chamber of said actuator, wherein said plate incorporates atleast one leak circuit connecting one of said control paths to said tankoutlet, said circuit in which is positioned a calibrated nozzle.
 4. Aninterface plate for a servovalve according to claim 3, wherein saidplate incorporates two leak circuits comprising a calibrated nozzle,each said circuit connecting said first or second control path to saidtank outlet.
 5. An interface plate for a servovalve according to claim4, wherein said leak circuits is advantageously made in the form ofholes perpendicular to one another and to said transversal drill holescorresponding to said first and second paths.
 6. An interface plate fora servovalve according to claim 5, wherein the outward opening of saideach hole is stopped by a plug.
 7. An interface plate for a servovalveaccording to claim 3, wherein said nozzles are made in the form ofscrews having a calibrated axial orifice.
 8. An interface plate for aservovalve according to claim 4, wherein said nozzles are made in theform of screws having a calibrated axial orifice.
 9. An interface platefor a servovalve according to claim 5, wherein said nozzles are made inthe form of screws having a calibrated axial orifice.